Treating rubber to enhance fiber bonding

ABSTRACT

Fiber to rubber adhesion is enhanced by incorporating into the rubber a formaldehyde donor and a saturated polymer comprising alkylene bridged resorcinol. The saturated polymer results from introducing unsaturated radicals in the resorcinol nucleus.

United States Patent [1 1 [111 3,816,361 Morita 1*June 11, 1974 [5 TREATING RUBBER TO ENHANCE FIBER [58] Field of Search 260/3, 845, 846, 38, 4

BONDING 75 Inventor: Eiichi Morita, Copley, Ohio [561 References CM [73] Assignee: Monsanto Company, Stv Louis, Mo. 2 801 980 ing? SZ I PATENTS 260/4 p c I Notice: The portion of the term of this 3.507,689 4/l970 Freytag 260/845 patent subsequent to Feb. 22, 1989, 3598.690 8/197l Danielson 260/3 has been 3,638,702 2/I972 Endter t 260/3 [22] F! d J 26 1972 3,644,268 2/1972 Morita 260/845 1e an. 21 App} 221 105 Primary Examiner-John C. Bleutge Related U.S. Application Data 57] ABSTRACT [63] Continuation-impart of Ser. No. 60,161, July 31, Fiber to rubber adhesion is enhanced b y mcorporatrng into the rubber a formaldehyde donor anda saturated polymer comprising alkylene bridged resorcinol. The [52] saturated polymer results from introducing unsatu- 260741 5 A 260N545 2O/846 1 rated radicals in the resorcinol nucleus. [51 Int. Cl. C08g 37/16, C08d 9/02, C08d 9/04 7 Claims, N0 Drawings TREATING RUBBER TO ENHANCE FIBER BONDlNG This application is a continuation-in-part of application Ser. No. 60,161 filed July 31, 1970 now US. Pat. 5 ducted und r a di nditions. When using the halo- N 3,644,268 iss d F b, 22, 1972 Thi i v ti r olefins, no additional acid is required since hydrogen lates to methods of treating rubber to enhance the a ide 8 a y-pr duct which maintains acidic Condibonding to fiber reinforcing elements and to the rubber tions in the reaction mixture. An olefin of three to 10 products so obtained. carbon atoms is preferred. The addition of other cata- 10 lysts is not necessary but may be used if desired. Exam- BACKGROUND OF THE INVENTION ples of other catalysts are sulfuric acid, acid clay, zinc The addition to rubber of silica, resorcinol and hexachloride and cuprous chloride. In the presence of cumethylenetetramine or other formaldehyde donor prous chloride alkenyl resorcinols form under mild reyields rubber compositions having increased affinity for action conditions and heating in the presence of resorfiber reinforcing elements. The treatment of rubber incinol easily effects an exothermic reaction resulting in stead of the fiber for preparing fiber to rubber bonded formation of the adhesive. composites has a number of advantages and this inven- Halo-olefins suitable for the practice of this invention tion is concerned with improvements in treating the are illustrated by 3-chloropropene, 3-chloro-l butene, rubber component although it may be practiced in con- 4-chloro-l-butene, l-chloro-Z-butene, 3-chloro-2- junction with treated fiber if desired and further imy p p -P 5-Ch 0r0-2- provements may sometimes be obtained thereby. pentene, 4-ehloro-2-methyI-Z-butene, 4-chloro-lhexene, 6-chloro-l-hexene, 2-chloro-3-hexene, 1-

SUMMARY OF THE INVENTION chloro-3-hexene and their halo counterparts in place of Adhesion of fiber to rubber is promoted by incorpoo nerating into the rubber :1 formaldehyde donor and an es- Examples of Suitable dihalo-olefins are sentially saturated polymer of resorcinol and an unsatu- P P pr pene, ,3- Chl0r0-2- rate. The presence of the said polymer in the rubber bulefle, 1,4-diCh10l'0-2-bl1tene, L also promotes building tack. The polymers contain al- 1,4-diChl0f04-butefle, 3 6, ,-5- kylene diresorcinol units comprising alkylene bridged dichlofo-l'pemeney lr3-dichlorol'pemene, resorcinol of two or more resorcinol units. dichlofo-z-pemener -P The unsaturate-resorcinol polymers characterized by dlchloro'zpemenew Y resorcinol units may be produced by the acidic conden- Ladichlofwbhexene, 1,3-diChl0f0-3-heXene, sation of resorcinol with an unsaturate. The alkylene dichlol'o'2,3dimethylj2-butene and theif'halo Counterbridge may be derived from an unsaturate selected P s Other than chlormef the group Consisting f (1) a h l l fin f three It IS understood that the halo-olefinrea'ctant must to 10 carbon atoms, (2) a dih l l f f three to 0 have at least one reactive halogen, preferably an allylic carbon atoms, (3) an acyclic or cyclic diolefin of three halogen to 10 carbon atoms or (4) an alkine of two to 10 carbon Examples of Sultable d101efin5 are Propadlene, atoms. Acidic conditions favor introduction of an unbutadlene; 13'Pemad1ene, f y fisaturated group into the resorcinol nucleus'and further lvs'helfadlenev l 'P l y 3- condensation occurs until essentially no unsaturation Pentadene, lfifoctadlenei 5r7'dlmethyl'lafioctadlene, remains 1,5-cyclooctadtene and 1,4:cyclooctad1ene.

Generally, the reaction may be effected between Examples of Sultable alkmes are acetylene, P y and 150C. preferably by adding the unsaturate under (anylene), l'butyne and z'bulyne' acidic conditions to resorcinol. Hig her temperatures 45 DESCRIP-HON OF PREFERRED EMBODIMENTS are preferred because the reaction is completed in a 1 shorter time. The reaction may be carried out by add- A Solutlon of 220 grams (two moles) of resorcmol m ing the unsaturate to molten resorcinol, but it is gener- 0 of Xylene Prepared and heated to ally more convenient to conduct the reaction with the 100 T 9 Any] Chlonde Is added ld after the resorcinol in an inert solvent. The use of a solvent aids 5O reactlon ls (fomplete the upper Solvent layer decanted in mixing the reactants, provides a uniform reaction h resldqal soivem removed by heatmg the temperature and permits easy removal of by-products. mammg p "T m vacuo' m three A number of solvents are suitable reaction media; the preparatlons whlch the anyl chionde Vaned as only requisites are that the solvent does not react with lows any of the starting materials or products of the reaction Allyl Feed Wt. of Reaction and is easily removed from the final product. Xylene is Ch'mide Time Healmg Time Pmducv an excellent solvent for this purpose. 1 mole 85 min, 4 200 The mole ratio of unsaturate to resorcinol is 0.5 to 2 moles 3 rs- 5.5 hrs 256 2.0 moles per mole of resorcinol. The unsaturate is ei- 3 moles 5 299 ther an alkine or olefin having two or more reactive sites, one of which is an ethylenically unsaturated bond. The apparent molecular weight distribution analyzed More specifically, a straight, branched chain, or cyclic by gel permeation chromatography is summarized bediolefln may be used, or a monoor dihalo-olefin, low:

Allyl 7n Apparent 7c Apparent Apparent 7r Apparent Apparent Chloride MW I MW 232 MW 456 MW 675 Avg. MW

I mole 2 40 26 17 15 (I000) 2 moles 3 28 l9 16 34 1200) 3 moles 4 l5 l3 13 55 ([500) When using an unsaturate having no halogen present such as an alkine or diolefin hydrocarbon, it is necessary to add a sufficient quantity of an acid, such as hydrogen chloride, to assure that the reaction is con The relative adhesion characteristics between fiber and vulcanized rubber product are determined by measuring the force required to pull a treated cord embedded in a strip of vulcanized rubber prepared from the foregoing base stock. The test is called an H-test and derives its name from the shape of the rubber cord article formed in the vulcanization mold. To the base stock is added 2.5 parts of resorcinol or 2.5 parts of the satutaining the allyl chloride resorcinol reaction product as compared to the base stock alone is shown by the fo1- lowing.

H-Test Adhesion of Untreated Cord (lbs) Addition to Base Stock Rayon Nylon None 6.7 3.3 Allyl chloride 0.65/resorcinol 1.0 24.0 22.3 Allyl chloride 1.0/resorcinol 1.0 25.1 22.1 Allyl chloride 2.0/resorcino1 1.0 7.8 4.2

Although it is preferable for obtaining maximum adhesion for the stocks to contain silica, the invention is not limited thereto since cord to rubber adhesion is improved in the absence of silica. A rubber stock is prepared similar to the previously described recipe except 15 additional parts carbon black are used in place of the silica. The other ingredients are the same except for hexamethylenetetramine, which is added in the indicated amounts as shown below.

Test 1 2 3 4 Mastcrbatch 173.8 173.8 173.8 173.8 Allyl chloride 1.0/resorcinol 1.0 2.5 2.5

reaction product I Hexamethylenetetramine 1.6 1.6

Cord

l'l-Test Adhesion to Polyester (lbs) Untreated 1000/2 polyester Treated 1000/2 polyester IAN rated alkylene di-resorcinol polymer prepared from ally] chloride and resorcinol in the ratio indicated in the table below. The base stock alone serves as control. Polyester cord is embedded in the rubber and is cured in the conventional H-test sample mold having rubber strip channels three-eighths-inch wide by 0.1 inch deep and separated from one another by one-fourth-inch. In one series of tests thecord embedded in the rubber is untreated. 1n the second series of tests the cord is coated or dipped in a solution of the same material as added to the base stock. Thus, the cord is treated with allyl chloride/resorcinol (1.0 to 1.0 mole ratio) reaction product and embedded in a base stock to which has been added an ally] chloride-resorcinol reaction product. The results are recorded below.

HTest Adhesion to Polyester (lbs) Allyl chloride 2.0/resorcinol 1.0

Cords treated with other treating agents, for example RFL, give improved adhesion values when the polymers of this invention are added to the rubber stock.

The adhesion of rayon and nylon to the stocks con- The unsaturate-resorcinol polymers are good tackifiers for synthetic elastomers. Natural rubber has sufficient tack to enable fabrication of products without layer separation before vulcanization. However, many synthetic elastomers are so deficient in tack that products cannot be fabricated without using tackifiers to enhance the adhesion of the components.

The tackifying property of the instant polymers is illustrated by comparing the tack of a styrene-butadiene copolymer stock with the tack of the same stock containing the unsaturate-resorcinol' polymer. The tack properties are determined by means of a Skewis tackmeter by the method described by J. D. Skewis, Rubber Chem. Technol. 38, 689 (1965). The values obtained are the time in seconds which is required to separate two specimens of the test material. Longer times are indicative of improved cohesion. The values shown below are the average of five determinations. Sample A comprises parts (all parts by weight) styrenebutadiene copolymer, 52 parts HAF carbon black and 10 parts high aromatic processing oil. Sample B comprises, in addition to the same ingredients as in Sample A, 5 parts of allyl chloride 1.0/resorcinol 1.0 reaction product.

Sample Tack (sec.)

The adhesive of this invention maybe used with natural rubber, synthetic rubber having sufficient unsaturation to enable sulfur vulcanization, or mixtures thereof. Examples of suitable synthetic rubbers are styrenebutadiene copolymer, isobutylene-isoprene copolymer, ethylene-propylene-diene terpolymers, butadieneacrylonitrile copolymer, polymers of chloroprene and synthetic polyisoprene. The polymers of this invention may be advantageously used in rubber stocks containing the commonly used accelerators, antidegradants, fillers and reinforcement agents. The amount of polymer required depends upon a number of factors but generally falls within the range of 0.5-10.0 parts per 100 parts elastomer.

Any formaldehyde donor which upon heating releases formaldehyde or furnishes radicals capable of forming methylene bridges is suitable for the practice of this invention. Examples of such materials are hexamethylenetetramine, hexamethoxymethylmelamine, cyclotrimethyltriamines and [(hydroxymethyl)ethylidc ne] alkylamines.

Other fibers than those particularly mentioned may be incorporated into rubber stocks prepared according to this invention. Examples are fibers of cotton, wool, wood cellulose, glass, aluminum, copper, tin, steel, brass plated steel and aluminum-steel alloys. The preparation of aluminum-steel alloy fibers and stainless steel fibers useful for making reinforced rubber articles is described in British Pat. No. 1,153,577, May 29, 1969.

EXTENDED DISCLOSURE For the practice of this invention, any olefinic reactant which introduces an unsaturated radical of three to carbon atoms into the nucleus of the resorcinol which unsaturated radical further condenses producing saturated resorcinol polymer having alkylene bridges of at least two carbon atoms is suitable. In addition to unsaturates previously disclosed, suitable unsaturateresorcinol polymers characterized by resorcinol units connected by alkylene bridges may also be prepared by the acidic condensation of resorcinol and olefinic alcohols or olefinic alcohol precursors. Branched or unbranched olefinic alcohols of three to 10 carbon atoms having at least two reactive sites are satisfactory. A difunctional alcohol is an alcohol having one hydroxy radical as one reactive site and one olefinic bond as' the other. A trifunctional alcohol may have either two hydroxy radicals and one olefinic bond or one hydroxyl radical andtwo olefinic bonds. it is believed that the unsaturate-resorcinol polymers are the same regardless of whether the alkylene bridge is derived from a haloolefin, diolefin or an olefinic alcohol. Representative examples of unsaturated alcohols which are satisfactory unsaturate reactants are allyl alcohol, methallyl alcohol, crotyl alcohol (Z-buten-l-ol), cinnamyl alcohol, 1,5-dimethyl-4-hexenl-ol, l-methyl-2-buten- 1 -ol, 3-hexen-1-ol, 4,6-dimethyl-l-hepten4-ol, 3-octen-lo1, 2,2-dimethyl-3-hexen-l-ol, 3,7-dimethyl-6-octen-lol, 3,7-dimethyl-2,6-octadiene-l-ol, 3,7-dimethyl-l,6- 0ctadiene-3-ol and 3(4-hydroxy-3-methoxy-phenyl)-2- propen- 1 -ol( coniferyl alcohol).

The term olefinic alcohol precursor means unsaturated esters or unsaturated ethers which upon acid hydrolysis yield olefinic alcohols. Formate, acetate, propionate and butyrate esters of any of the above illustrated unsaturated alcohols are satisfactory, for example, allyl formate, allyl acetate, allyl propionate, methallyl acetate, crotyl acetate and the like. Symmetrical and unsymmetrical ethers are satisfactory provided that the ether gives two moles of unsaturated radical when introduced into. the resorcinol nucleus wherein each mole may be the same or different. Illustrative examples of satisfactory ethers are allyl ether, bis( 2- methylallyl)ether, allyl-3-methyl-3-butenyl ether and 2-butenyl-l-methylallyl ether. It is understood that the invention is not limited to the unsaturate reactants disclosed for illustrative purposes but that the invention is applicable to any olefinic alcohol of three to 10 carbon atoms or olefinic alcohol precursorv which yields said alcohols of three to 10 carbon atoms. Further examples wouldonly unduly extend the disclosure without contributing to a better understanding of the invention. Many olefinic alcohols and alcohol precursors are known and may be readily found in the literature.

The mole ratio of unsaturate-to-resorcinol is the same for olefinic alcohols and alcohol precursors as other unsaturate reactants previously discussed. Typical preparations using alkyl alcohol as unsaturate are illustrated below.

Resins are prepared by adding dropwise over a period of -90 minutes 43.5 g of allyl alcohol to a mixture comprising 1 10 g of resorcinol and 1-8 g of acid resins contain about 17-24 percent free resorcinol.

A rubber stock is prepared similar to the previously described recipe except the N-cyclohexyl-Z-benzothiazolesulfenamide is replaced with 0.5 parts of N- tert-butyl-2-benzothiazolesulfenamide. The adhesion of nylon 840/2 tire cord and rayon 2200/3 tire cord to stocks containing 2 parts of the unsaturated resorcinol polymer-is compared to the adhesion of the same tire cords in the base stock alone.

H-Test Adhesion of Untreated Cords (lbs) Addition to Base Stock Rayon Nylon None 5.0 3.6 Allyl Chloride 1.0/resorcinal 1.0 22.2 19.3 Allyl alcohol 0.75/resorcinal 1,0 229* 17.8*

The average of the values obtained for four separate preparations of the polymers.

Although the invention has been illustrated by typical examples, it is not limited thereto. Changes and modifications of the examples of the invention herein chosen for purposes of disclosure can be made which do not constitute departure from the spirit and scope of the invention.

The embodiments of the invention'in which an exclusive property or privilege is claimed are defined as follows:

l. The method of making fiber reinforced rubber having the fiber bonded to the rubber which comprises incorporating fiber and an adhesion-enhancing amount of a combination comprising a formaldehyde donor and an essentially saturated polymer of resorcinol resulting from introducing olefinic unsaturated radical of three to 10 carbon atoms into the nucleus of resorcinol under conditions of further condensation said polymer comprising resorcinol units connected by alkylene bridges of at least two carbon atoms, into a vulcanizable rubber stock, said polymer being present in the amount of 0.5l0.0 parts per 100 parts rubber and heating to form a vulcanized fiber bonded rubber product.

2. The method of claim 1 in which the polymer is prepared by reaction of 0.5 to 2 moles of unsaturate per mole of resorcinol.

3.The method of claim 2 in which the unsaturate is selected from the group consisting of (l) halo-olefin,

(2) dihalo-olefin, (3) acyclic or cyclic diolefin and- (4) olefinic alcohol or olefinic alcohol precursor.

- 4. The method of claim 3 in which the fiber is selected from the group consisting of polyester, rayon and nylon.

5. The method of claim 3 in which the polymer is the reaction product of about 0.5 to about 1 mole of allyl chloride per mole of resorcinol.

6. The method of claim 3 in which the polymer is the reaction product of about 0.5 to about 1 mole of allyl alcohol per mole of resorcinol.

7. The method of claim 3 in which the rubber stock contains silica. 

2. The method of claim 1 in which the polymer is prepared by reaction of 0.5 to 2 moles of unsaturate per mole of resorcinol.
 3. The method of claim 2 in which the unsaturate is selected from the group consisting of (1) halo-olefin, (2) dihalo-olefin, (3) acyclic or cyclic diolefin and (4) olefinic alcohol or olefinic alcohol precursor.
 4. The method of claim 3 in which the fiber is selected from the group consisting of polyester, rayon and nylon.
 5. The method of claim 3 in which the polymer is the reaction product of about 0.5 to about 1 mole of allyl chloride per mole of resorcinol.
 6. The method of claim 3 in which the polymer is the reaction product of about 0.5 to about 1 mole of allyl alcohol per mole of resorcinol.
 7. The method of claim 3 in which the rubber stock contains silica. 